Optical link has replaced electrical link for long distance communication over the past decades, and recent computation and communication systems place huge demands on increasing speed and data volume. To enlarge the transmission capacity, an efficient bandwidth utilization method, wavelength division multiplexing (WDM) is widely used now by transmitting several channels at different optical wavelengths into a single optical channel.
Wavelength division multiplexing (WDM) is a technology that multiplexes optical signals with different wavelengths into a single optical fiber or other destination, and later spatially disburses the multi-wavelength light from a fiber optic waveguide into individual wavelength bands, and direct them to individual fiber optic waveguide output lines, light detectors, etc.
Since different modes of the fiber travel at different speeds, multimode fibers have the difficulty to couple the different wavelength optical signals in parallel and transmit them simultaneously. Single mode fibers can give a higher transmission rate and up to 50 times more distance than multimode due to that its small core and depressed dispersion, their ability to couple multiple wavelength optical signals simultaneously made them be widely used in WDM technology for long distance optical communication.
In fiber optical communication applications, aligning light source to optical fibers or other types of waveguide is always an important issue. Multimode fibers have the core size relatively large, at about 50 um, so the tolerances can be substantially loose. In single mode transmission, the light receiving region of a photodiode is tens of micron in diameter, the laser source typically has a mode size of only a few micron, and a core of an optical fiber just has approximate 8 um in diameter. Thus, the presence of a manufacture error in the optical transmitting and receiving module may result in a large loss of optical signals. Tolerances on the order of a tenth of a micron are strongly required, hence, the alignment is a difficult and complicit process in manufacture.
In CWDM transceiver modules, alignment among light source, fiber/wave guide, and detector has seriously impacted on signal transmission, especially the alignment to couple light sources to the single mode fiber which has a mode size of only 8 um in diameter. Again, the alignment is a difficult and complicit process in manufacturing. It is therefore desired to have a batch fabricated CWDM transmitter that can lower the cost, and an active alignment method implemented by integrated MEMS platform, which can increase the alignment accuracy and simplify the alignment process.